#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>

/* module config */
typedef struct {
    ngx_str_t  ed;
} ngx_http_sample_loc_conf_t;

static char *ngx_http_sample_echo(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
static void *ngx_http_sample_create_loc_conf(ngx_conf_t *cf);
static char *ngx_http_sample_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child);

/*
    directives
    nginx.conf
    location /echo {
        echo "this is a nginx sample module!";
    }
*/
static ngx_command_t  ngx_http_sample_commands[] = {
    {
        ngx_string("echo"),
        NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
        ngx_http_sample_echo,
        NGX_HTTP_LOC_CONF_OFFSET,
        offsetof(ngx_http_sample_loc_conf_t, ed),
        NULL
    },
    ngx_null_command
};

/* context of the module */
static ngx_http_module_t  ngx_http_sample_module_ctx = {
    NULL,                                  /* preconfiguration */
    NULL,                                  /* postconfiguration */
    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */
    NULL,                                  /* create server configuration */
    NULL,                                  /* merge server configuration */
    ngx_http_sample_create_loc_conf,       /* create location configration */
    ngx_http_sample_merge_loc_conf         /* merge location configration */
};

/* nginx module */
ngx_module_t  ngx_http_sample_module = {
    NGX_MODULE_V1,
    &ngx_http_sample_module_ctx,           /* module context */
    ngx_http_sample_commands,              /* module directives */
    NGX_HTTP_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};

/* handler function */
static ngx_int_t
ngx_http_sample_handler(ngx_http_request_t *r)
{
    ngx_int_t rc;
    ngx_buf_t *b;
    ngx_chain_t out;
    ngx_http_sample_loc_conf_t *slcf;

    slcf = ngx_http_get_module_loc_conf(r, ngx_http_sample_module);
    if (!(r->method & (NGX_HTTP_HEAD|NGX_HTTP_GET|NGX_HTTP_POST))) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    r->headers_out.content_type.len = sizeof("text/html") - 1;
    r->headers_out.content_type.data = (u_char *) "text/html";
    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_length_n = slcf->ed.len;

    if (r->method == NGX_HTTP_HEAD) {
        rc = ngx_http_send_header(r);
        if (rc != NGX_OK) {
            return rc;
        }
    }

    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));

    if (b == NULL) {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "Failed to allocate response buffer.");

        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    out.buf = b;
    out.next = NULL;
    b->pos = slcf->ed.data;
    b->last = slcf->ed.data + (slcf->ed.len);
    b->memory = 1;
    b->last_buf = 1;

    rc = ngx_http_send_header(r);

    if (rc != NGX_OK) {
        return rc;
    }

    return ngx_http_output_filter(r, &out);
}

static char *
ngx_http_sample_echo(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_core_loc_conf_t  *clcf;
    clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
    clcf->handler = ngx_http_sample_handler;
    ngx_conf_set_str_slot(cf, cmd, conf);

    return NGX_CONF_OK;
}

static void *
ngx_http_sample_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_sample_loc_conf_t  *conf;
    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_sample_loc_conf_t));

    if (conf == NULL) {
        return NGX_CONF_ERROR;
    }

    conf->ed.len = 0;
    conf->ed.data = NULL;

    return conf;
}

static char *
ngx_http_sample_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_http_sample_loc_conf_t *prev = parent;
    ngx_http_sample_loc_conf_t *conf = child;

    ngx_conf_merge_str_value(conf->ed, prev->ed, "");

    return NGX_CONF_OK;
}
